1. Field of the invention.
The present invention relates to a stabilizer for a total or partial middle-ear prosthesis ending in a columella bearing against the base of the stapes.
The natural mechanism for the transmission of sonic vibrations from the tympanum to the inner ear functions via the ossicular chain. The fenestra of the vestibule, in which the stapes (the smallest of the ossicles) lies, provides communication between the middle ear and the inner ear. The transmission mechanism functions through three articulated ossicles; the malleus, the incus, and the stapes, which amplify the vibrations of the tympanum for transmission of sound to the inner ear.
Numerous pathologies of the middle ear (chronic otitis media in different forms, injuries, sequelae of previous operations) may result in dysfunction of the tympano-ossicular complex. This dysfunction entails a hearing impairment in the form of conduction deafness, that is to say impairment of the auditory function characterized by failure to achieve correct transmission of the sound message propagated from the external ear to the inner ear.
If the middle ear, which functions essentially as an acoustic impedance transformer, cannot perform this function, the cochlear input signal is diminished and so-called conduction deafness results.
Such conduction deafness is principally associated with damage to the tympanum (perforation of the tympanum), or with injury to the ossicular chain (ankylosis or ossicular lysis).
The present invention relates more particularly to a stabilizer for prostheses intended for the reconstruction of the ossicular chain for the purpose of safeguarding transmission of sound.
The reconstruction of the different bony parts of the middle ear or external ear is possible by means of ossicular alloplasty (ossicle taken from a donor) or by means of ossicular autoplasty (removal of one of the patient's ossicles, remodelling and restoration of tympano-ossicular continuity), or, more recently, by fitting a prosthesis made of a so-called biocompatible material. In recent years use has in particular been made of porous polyethylenes (such as the porous polyethylene marketed under the trade mark Proplast.RTM.) or of biocompatible ceramics, particularly bioactive biocompatible ceramics (such as that marketed under the trade mark Ceravital.RTM.), the slow superficial dissolution of which permits reossification and excellent contact between the tympanum or the neotympanum and the ceramic prosthesis.
2. Description of the prior art.
The reconstruction of the sound transmission mechanism in the middle ear by the implantation of biocompatible prostheses is well known.
Various forms of ossicular prostheses exist. A distinction is in particular made between so-called total prostheses and so-called partial prostheses. A total prosthesis is fitted directly between the tympanum (or the neotympanum) and the base of the stapes. A partial prosthesis is intended to replace only a part of the ossicular chain (the remainder of the ossicular chain being intact). The principal known partial prostheses are those intended to be fitted between the tympanum (or the neotympanum) and the head of the stapes, and also those partial prostheses which are intended to be fitted between the end of the process of the incus and the base of the stapes.
Most total prostheses used at the present time are prostheses functioning in the form of columellae, that is to say the entire ossicular chain (malleus, incus, stapes) is replaced by a single prosthesis interposed directly between the tympanum or the neotympanum and the base of the stapes (see for example U.S. Pat. No. 4,510,627 and FIG. 2).
The Applicant's co-pending patent application of the same date describes an articulated total prosthesis ending in a columella bearing against the base of the stapes. This columella replaces the stapedial arch.
It often happens that of the ossicles of the middle ear the malleus and the incus are still intact, while the stapedial arch of the stapes is damaged. The arch is then also replaced by a small columella (see U.S. Pat. No. 3,196,462 and FIG. 3, and also U.S. Pat. No. 3,391,648 and FIG. 4).
Depending on the type of prosthesis, the columella of biocompatible material may be of porous material, such as polyethylene, of polytetrafluoroethylene, or of ceramic or bioactive ceramic material (for example Ceravital.RTM.).
In all cases where the middle-ear prosthesis ends in a columella bearing against the base of the stapes it is impossible to fasten the end of the columella in a mechanically secure manner on the base. There is consequently a risk of lateral displacement of the columella and a risk of loss of contact with the base as the result of contraction of the neotympanum during the process of postoperative cicatrization, or for any other reason, with loss of sound transmission.